When I tested
SeeSaw a while back I was fairly impressed. How much effect it has seems to depend on the source quality, although I only ran a few encodes with it so I may have no idea what I'm talking about. One of my test 720p to 480p encodes using a fairly average quality source, turned out surprisingly well. In some areas the 480p encode looked better than the source.
I don't actually use
SeeSaw. It's nice, but it slows the encoding process down quite a lot.